While the results of previous research demonstrates the feasibility, acceptability, and promising efficacy of clinical physical activity interventions, studies to date with older samples suggests that more comprehensive interventions may be necessary to achieve physical activity behavior change among sedentary, older adults. We propose conducting a randomized, controlled Physical Activity Counseling Trial (PACT) within a hospital-based, primary care setting with 150 sedentary, adults aged 50 and older to increase physical activity. Specific aims of the project include: To experimentally evaluate whether the PACT intervention can increase physical activity by middle-aged and older persons compared with a control sample of older persons who receive activity advice from a physician; To experimentally evaluate whether the intervention changes stage-of- readiness among intervention subjects relative to controls. Within this primary care setting, Roybal Center staff will implement a 6- month intervention based on a synthesis of behavior change frameworks that has yielded promising results in similar applications. Intervention components include: physician advice, clinic support systems, a motivational videotape, health educator delivered counseling, behavior change reinforcement materials, and follow-up contacts. This experimental intervention will be compared with a control condition of brief provider advice only. The primary outcome variable is overall physical activity level as measured by a Caltrac accelerometer. The secondary outcome is stage of readiness to become physically active. Impact on study outcomes will be evaluated by comparing baseline values with values at the 6-month follow-up. The proposed investigation will extend existing knowledge by adapting previous physical activity interventions for use with sedentary older persons and assess its feasibility and efficacy within a hospital- based, primary care context.